A way to shed light on the mysteries of our digestive tract.

Digestion is something of a black box. We know food gets put through a physical and chemical pulverization to make it easier to extract nutrients before we get rid of the waste. But there are all sorts of variances in each of our own unique digestive tracts. So when someone’s digestion goes awry, it’s hard to tell what exactly is wrong or how to fix it.

The capsule and transmitter. (Kalantar-Zadeh et al., 2018)

One potential way to shed light on the (literally and figuratively) dark, bacteria-ridden tube that makes up our digestive tract is to send an electronic pill down it.

In a paper published Monday in Nature Electronics, a group of researchers describe a successful study in which five participants swallowed a capsule that could track aspects of the gaseous content in their gut, and relay that information to an external sensor every five minutes. They could measure the time the capsule took to go through the gastrointestinal system, and could even pick up on increases in fiber content in participants’ diets over three days. Ideally, the capsules could one day be used as a diagnostic tool for digestive disorders, or a monitoring tool to see if a dietary change are an effective treatment.

(Kalantar-Zadeh et al., 2018)

The capsules are an inch long and just under half an inch wide, which is as large as swallowable pills can get. Within each, there’s a tiny thermometer, radio transmitter (to send information to an external device that fits in a pocket), a battery, and sensors that detect oxygen, hydrogen, and carbon dioxide within the gut. We’re full of other gases including nitrogen, methane, and what the authors of this paper call “odoriferous gas and vapor species” (AKA farts), but doctors can learn a lot by tracking the three gases these capsules can sense.

Oxygen is used like a locational device: it shows where the body is breaking down contents aerobically (with oxygen) or anaerobically (without it). Carbon dioxide levels can give insight into a person’s gut microbiome: the bacteria in our gut microbiomes release CO2 as a byproduct of their metabolism, and the right amount of CO2 in the gut shows our microbiome is alive and thriving. (We all need these microbes, although too much of certain species can be a bad thing.) Hydrogen is possibly the most important gas to track from a clinical standpoint, because it shows when foods are being broken down through fermentation. That happens when the normal gut processes fail to break down food, and is a sign more generally that a patient’s body can’t handle certain foods.

This study was small, and just a proof of concept. But it was highly successful: The capsules make the journey through the digestive tract in about a day (the researchers tracked the progress of the capsule using an ultrasound) before they are excreted like any other indigestible food. The researchers took fecal samples and were able to confirm food was being broken down as the capsules reported.

Two of the patients were put on high-fiber (about 33 grams per day), and two were put on low-fiber diets; the fifth was tested at both a low- and high-fiber diet. In all of them, data from the capsule reflected expected changes in the gut microbiomes of a high-fiber diet: different species flourished after a couple of high-fiber days. Fiber is one of those components of food that gut bacteria love—after a couple of days eating more fiber, microbiomes are typically more robust, which is healthier for their host humans.

In addition, none of the participants experienced any adverse effects from these capsules. That included Kourosh Kalantar Zadeh, an engineering professor at the Royal Melbourne Institute of Technology and lead author of the paper, who was happy to test out his own device, according to NPR.